Missouri law enforcement agencies could track people's cellphone signals during emergencies more easily under a measure signed by Gov. Jay Nixon.

The legislation enacted Friday requires phone companies to cooperate with police by tracking cellphone signals of 911 callers, or by pinging a phone's location when there is danger of death or serious physical injury.

The law was prompted by the 2007 killing of 18-year-old Kelsey Smith, who was abducted from a shopping center parking lot in Overland Park, Kan. Her body was found four days later in a wooded area in Missouri.

Sponsoring House member Jeanie Lauer, a Republican from Blue Springs, has said Smith might have been found faster if authorities had been better able to track her cellphone signals.